Tumor necrosis factor receptor cross-talk

Extensive research has been performed to unravel the mechanistic signaling pathways mediated by tumor necrosis factor receptor 1 (TNFR1), by contrast there is limited knowledge on cellular signaling upon activation of TNFR2. Recently published data have revealed that these two receptors not only function independently, but also can influence each other via cross-talk between the different signaling pathways initiated by TNFR1 and TNFR2 stimulation. Furthermore, the complexity of this cross-talk is also dependent on the different signaling kinetics between TNFR1 and TNFR2, by which a delicate balance between cell survival and apoptosis can be maintained. Some known signaling factors and the kinetics that are involved in the receptor cross-talk between TNFR1 and TNFR2 are the topic of this review.     

Tumor necrosis factor family ligand-receptor binding

Ligands and receptors of the tumor necrosis factor (TNF) superfamily have pivotal roles in the development and function of the immune system. The growing pool of data on TNF from structural and biochemical studies suggests that the higher order clustering of TNF family ligands could play an essential role in signal transduction initiation for this superfamily. The identification of new structural modules of TNF family receptors, as well as interaction modes between ligands and receptors, greatly expands our knowledge of how TNF family ligands and receptors determine specificity among diverse family members and between two closely related family members.     

Tumor necrosis factor induction by Sendai virus

Supernatants of peripheral blood mononuclear leukocytes (PBMC) treated with Sendai virus were found to exert significant cytotoxic effects mediated by leukocyte-produced proteins distinct from interferon. Fractionation of the PBMC into adherent and nonadherent cells indicated that these virus-induced cytotoxins (CTX) were produced primarily in the mononuclear phagocytes. Cells of the monocyte-like U937 line pretreated with 4 beta-phorbol-12-myristate-13-acetate could also be induced with Sendai virus to produce CTX. The nonadherent mononuclear cells of the peripheral blood responded poorly to the virus with regard to CTX production, even though they could be induced to produce CTX with phytohemagglutinin (PHA). With the use of monospecific antibodies to tumor necrosis factor (TNF) and to lymphotoxin (LT), it was found that TNF is the major CTX produced by PBMC and by the U937 cells after 24 hr stimulation by the virus, whereas LT is not induced under these conditions to any measurable extent. TNF was also found to be produced in significant amounts together with LT upon stimulation of the nonadherent fraction of the PBMC by PHA. These findings indicate that besides bacterial lipopolysaccharides, other biological agents including viruses can be effective inducers of tumor necrosis factor, suggesting implications regarding the physiologic role of this protein.     

Tumor necrosis factor as a pharmacological target

As indicated by its name, tumor necrosis factor (TNF), cloned in 1985, was originally described as a macrophage-derived endogenous mediator that can induce hemorrhagic necrosis of solid tumors and kill some tumor cell lines in vitro. Unfortunately, its promising use as an anticancer agent was biased by its toxicity, which was clear soon from the first clinical trials with TNF in cancer. Almost at the same time TNF was being developed as an anticancer drug, it became clear that TNF was identical to a mediator responsible for cachexia associated with sepsis, which was termed cachectin. This research led to the finding that TNF is, in fact, the main lethal mediator of sepsis and to the publication of a huge number of articles showing that TNF inhibits the toxic effects of bacterial endotoxins, which are now described as systemic inflammatory response. Although the clinical trials with anti-TNF in sepsis have not been successful thus far, undoubtedly as a result of the complexity of this clinical setting, these studies ultimately led to the identification of TNF as a key inflammatory mediator and to the development of anti-TNF molecules (soluble receptors and antibodies) for important diseases including rheumatoid arthritis and Crohn’s disease. On the other side, the mechanisms by which TNF and related molecules induce cell death have been studied in depth, and their knowledge might, in the future, suggest means of improve the therapeutic index of TNF in cancer.     

Tumor necrosis factor, cancer and anticancer therapy

Tumor necrosis factor (TNF) is being utilized as an antineoplastic agent for the treatment of patients with locally advanced solid tumors. However, its role in cancer therapy is debated. Although a large body of evidence supports TNF's antineoplastic activity, the cascade of molecular events underlying TNF-mediated tumor regression observed in vivo is still incompletely elucidated. Intriguingly, some pre-clinical findings suggest that TNF may promote cancer development and progression, which has led to propose anti-TNF therapy as a novel approach to malignancies. In the present work, we summarize the molecular biology of TNF with particular regard to its tumor-related properties, and review the experimental and clinical evidence currently available describing the complex and sometime conflicting relationship between this cytokine, cancer and antitumor therapy. Recent insights that might pave the way to further exploitation of the antineoplastic potential of TNF are also discussed.     

Tumor necrosis factor in human monocyte-mediated antitumor cytotoxicity

The WEHI-164 target cells pretreated with actinomycin D can be employed in a 7-hour 51Cr release assay that exhibits exquisite susceptibility for cytotoxic monocytes without contribution by natural killer cells. The system can be used either to detect cell-mediated monocyte cytotoxicity directly or to measure cytotoxic-factor activity in cell-free supernatants. Analysis of cytotoxic factor demonstrates molecular characteristics similar to tumor necrosis factor (TNF), and polyclonal as well as monoclonal antibodies specific for TNF can readily neutralize the monocyte-generated cytotoxic factor. In the cell-mediated approach, neutralization can be achieved as well, although somewhat higher amounts of antibody are required. Hence, the WEHT-164/actinomycin D system appears to detect monocyte cytotoxicity that is mediated by TNF.     

Tumor necrosis factor alpha induction in human monocytes

The present study was undertaken to assess the presence of tumor necrosis factor (TNF)-alpha mRNA and protein in circulating human blood monocytes and to study the TNF-alpha gene expression in human monocytes isolated by continuous Percoll gradient fractionation. The technique of RNA isolation directly from the blood samples was used to study TNF-alpha mRNA expression in circulating human blood leukocytes. It was shown that human blood leukocytes of healthy donors contained no presynthesized pool of TNF-alpha mRNA as well as no TNF-alpha protein. It was found that early pretreatment with cycloheximide interferes with TNF-alpha mRNA induction by Staphylococcus aureus.     

Tumor necrosis factor induces acute phase proteins in rats

Inoculation of WAG rats with recombinant mouse tumor necrosis factor results in a rapid and marked increase in several acute phase proteins in the serum (haptoglobin, alpha 1 acid glycoprotein, alpha 2 macroglobulin) and in the plasma (fibrinogen). We conclude that TNF may play an important role in the inflammatory response in vivo and possibly in the pathogenesis of inflammatory disorders.     

Tumor necrosis factor is critical to control tuberculosis infection

Tumor necrosis factor (TNF) is critical and non-redundant to control Mycobacterium tuberculosis infection and cannot be replaced by other proinflammatory cytokines. Overproduction of TNF may cause immunopathology, while TNF neutralization reactivates latent and chronic, controlled infection, which is relevant for the use of neutralizing TNF therapies in patients with rheumatoid arthritis.     

Tumor necrosis factor and interferon: cytokines in harmony

Individually, tumor necrosis factor (TNF) and the various interferons frequently display strong antiviral activities. Certain combinations of these cytokines, however, induce a synergistic antiviral state which is distinct from that induced by either one alone. This novel synergistic antiviral state likely occurs through several possible mechanisms, involves multiple signaling pathways, and inhibits a wider range of viruses than the individual cytokines alone. While underappreciated when first discovered, this synergistic phenomenon is proving to be of a much broader scope than initially thought. More work is needed to refine our understanding of this observation and its physiological implications for anti-pathogen responses.     

Tumor necrosis factor gene polymorphisms in breast cancer patients

Analysis of microsatellite TNFalpha marker and (-308(G/A) polymorphisms in promoter of TNFalpha gene was conducted in 167 patients with various types of sporadic breast cancer (BC) as well as in 139 healthy Russian donors. It was shown that frequency of allele 7 in TNFalpha microsatellite marker was significantly higher in BC patients than in healthy donors (17.9% versus 10.4%; P = 0.02) mainly due to the patients with invasive ductal BC (19.2% versus 10.4%; P = 0.008). The TNFalpha allele 9 was observed significantly more frequently in patients with invasive-ductal cancer (6.4% versus 1%; P= 0.01). The studies of-308(G/A)TNFalpha polymorphism in BC patients and healthy donors have shown no differences in the distribution frequency of highly secreted allele (-308A)TNFalpha. However, invasive lobular BC patients carrying (-308AG)TNFalpha genotype were observed significantly more frequently than invasive-ductal BC patients carrying the same allele (34.0 versus 17.3%; P = 0.034). Thus it has been shown for the first time that invasive-ductal and invasive-lobular BC patients differ in distribution of TNFalpha and -308(G/A)TNFalpha alleles.     

Tumor necrosis factor induces activation of mitochondrial succinate dehydrogenase

We have studied TNF-induced changes in mitochondrial enzymes. One enzyme, succinate dehydrogenase (SDH), is specifically activated in TNF sensitive cells including U937 (human monocytic), WEHI-164 (murine fibrosarcoma), and ME-180 (human cervical carcinoma). SDH is activated by TNF concentrations which also cause cytolysis, however the enzyme activity is elevated several hours before maximum cytotoxicity is observed. In contrast, TNF does not activate SDH in TNF resistant variants derived from U937 and WEHI-164.     

Tumor necrosis factor provokes superoxide anion generation from neutrophils

We report that tumor necrosis factor (TNF) provokes superoxide anion generation from human neutrophils. Superoxide anion generation was provoked at TNF concentration of 1 X 10(-11) M and maximal generation was attained at TNF concentration of 1 X 10(-9) M. We also show that movements of intracellular calcium may mediate the TNF-stimulated superoxide anion generation because 8-(diethylamino) octyl 3,4,5-trimethoxybenzoate hydrochloride--but not extracellular EGTA--inhibited the generation of superoxide anion. These results suggest that TNF may mediate some mechanisms of host defense by provoking superoxide anion generation from neutrophils.     

Tumor necrosis factor and its induction by bacterial endotoxins

Using suitable immunomodulators (Corynebacterium parvum vaccine, Zymosan or muramyl dipeptide), lipopolysaccharides (LPS) from various members of the family Enterobacteriaceae (Escherichia, Salmonella, Serratia, Shigella) were tested on rabbits in relation to the production of tumor necrosis factor (TNF). TNF was determined by means of the serum titration of L-929 cell cultures in the presence of Actinomycin D, this with resulting titres of 3.2 x 10(3) to 5.1 x 10(4) IU TNF/ml. Analogous titres were noted after the action of denatured LPS (ie LPS subjected to alkaline hydrolysis or H2O2).     

Tumor necrosis factor gene polymorphisms in breast cancer patients

Analysis of microsatellite TNFa marker and (?308(G/A) polymorphisms in promoter of TNFa gene was conducted in 167 patients with various types of sporadic breast cancer (BC) as well as in 139 healthy Russian donors. It was shown that frequency of allele 7 in TNFa microsatellite marker was significantly higher in BC patients than in healthy donors (17.9% versus 10.4%; P = 0.02) mainly due to the patients with invasive ductal BC (19.2% versus 10.4%; P = 0.008). The TNFa allele 9 was observed significantly more frequently in patients with invasive-ductal cancer (6.4% versus 1%; p = 0.01). The studies of ?308(G/A)TNFα polymorphism in BC patients and healthy donors have shown no differences in the distribution frequency of highly secreted allele (?308A)TNFα. However, invasive lobular BC patients carrying (?308AG)TNFα genotype were observed significantly more frequently than invasive-ductal BC patients carrying the same allele (34.0 versus 17.3%; P = 0.034). Thus it has been shown for the first time that invasive-ductal and invasive-lobular BC patients differ in distribution of TNFa and ?308(G/A)TNFα alleles.     

Tumor necrosis factor inhibits human myogenesis in vitro.

We examined the effects of human recombinant tumor necrosis factor-alpha (TNF) on human primary myoblasts. When added to proliferating myoblasts, TNF inhibited the expression of alpha-cardiac actin, a muscle-specific gene whose expression is observed at low levels in human myoblasts. TNF also inhibited muscle differentiation as measured by several parameters, including cell fusion and the expression of other muscle-specific genes, such as alpha-skeletal actin and myosin heavy chain. Muscle cells were sensitive to TNF in a narrow temporal window of differentiation. Northern (RNA) blot and immunofluorescence analyses revealed that human muscle gene expression became unresponsive to TNF coincident with myoblast differentiation. When TNF was added to differentiated myotubes, there was no effect on muscle gene expression. In contrast, TNF-inducible mRNAs such as interferon beta-2 still responded, suggesting that the signal mediated by TNF binding to its receptor had no effect on muscle-specific genes after differentiation.